Ordinary utility power is subject to a number of problems. The first of these problems is outages, in which power is entirely interrupted to a customer for a period of minutes to days. Another problem is termed “brownouts”, in which power is supplied to a customer at a lower voltage than specifications would normally permit.
A customer may provide an auxilliary short-term power source to mitigate these problems. A common auxilliary power source is a generator, for example powered by a diesel fuel engine, which can be stared in the event of an outage or brownout. Another auxilliary power source that has become common in recent years is the Uninterruptible Power Supply, or UPS. UPS systems, rather than having a generator, typically utilize a solid-state inverter powered from batteries, lead-acid being a common battery type. For certain applications, such as powering resistive loads and nonelectronic loads, these systems may be adequate to retain electrical equipment functionality without large inconvenience.
Other problems may exist with ordinary utility power. Spikes and dips may occur, for example, through the switching of circuits and the powering of motors near the point of power consumption, or the switching of mains circuits in the power distribution network. Noise may also be introduced on the power lines by “dirty” electronics, motor brushes and modified-sine wave inverters. Variations in voltage level and frequency may also occur, particularly where power is supplied from an auxiliary generator. Power may be interrupted to important electronic equipment for periods in duration from tens of milliseconds to even seconds, which may be mitigated at the equipment level by large reserviour capacitors and other techniques. Electronic equipment may be supplied with overvoltage as well, which may lead to premature equipment failure.